Reforming catalyst system with differentiated acid properties

ABSTRACT

A catalyst system comprising a physical mixture of particles of a non-acidic large-pore zeolite containing a platinum-group metal and particles comprising a refractory inorganic oxide which is metal-free is effective for the reforming of a hydrocarbon feedstock. Reforming of paraffinic feedstocks to effect aromatization, particularly of a raffinate from aromatics extraction, provides improved activity in producing gasoline-range products when using the catalyst system of the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved catalyst system and process forthe conversion of hydrocarbons, and more specifically for the catalyticreforming of gasoline-range hydrocarbons.

2. General Background

The catalytic reforming of hydrocarbon feedstocks in the gasoline rangeis an important commercial process, practiced in nearly everysignificant petroleum refinery in the world to produce aromaticintermediates for the petrochemical industry or gasoline components withhigh resistance to engine knock. Demand for aromatics is growing morerapidly than the supply of feedstocks for aromatics production.Moreover, the widespread removal of lead antiknock additive fromgasoline and the rising demands of high-performance internal-combustionengines are increasing the required knock resistance of the gasolinecomponent as measured by gasoline "octane" number. The catalyticreforming unit therefore must operate more efficiently at higherseverity in order to meet these increasing needs for chemical aromaticsand gasoline-octane. This trend creates a need for more effectivereforming processes and catalysts.

Catalytic reforming generally is applied to a feedstock rich inparaffinic and naphthenic hydrocarbons and is effected through diversereactions: dehydrogenation of naphthenes to aromatics,dehydrocyclization of paraffins, isomerization of paraffins andnaphthenes, dealkylation of alkylaromatics, hydrocracking of paraffinsto light hydrocarbons, and formation of coke which is deposited on thecatalyst. Increased aromatics and gasoline-octane needs have turnedattention to the paraffin-dehydrocyclization reaction, which is lessfavored kinetically in conventional reforming than formation ofaromatics from naphthenes. Catalyst acidity, and particularly Bronstedacidity, has been considered to be adverse to enhanced paraffinaromatization.

The effectiveness of reforming catalysts comprising a non-acidicL-zeolite and a platinum-group metal for dehydrocyclization of paraffinsis well known in the art. The use of these reforming catalysts toproduce aromatics from paraffinic raffinates as well as naphthas hasbeen disclosed. Nevertheless, commercialization of thisdehydrocyclization technology has been slow following an intense andlengthy development period. Catalyst selectivity, stability, andsensitivity to contaminants such as sulfur offer potential forimprovement. Increased isomerization of residual paraffins and reduceddealkylation of alkylaromatics are goals within these broaderobjectives.

U.S. Pat. No. 4,191,638 (Unmuth et al.) discloses reforming with acatalyst combination comprising a zeolite and a conventional catalyst.Both the zeolite and the conventional catalyst comprise a platinum-groupmetal and a halide, and thus are acidic. Examples of zeolites are ZSM-5,CaY and TEA-mordenite.

U.S. Pat. No. 4,418,006 (Kim et al.) discloses a physical particle-formmixture of a first catalyst which is free of zeolite and comprises anoble metal and halogen and a second catalyst comprising a zeolite andnon-noble metal free of noble metals. The preferred catalyst componentscomprise platinum on chlorided alumina and Re, Ga or W on mordenite.

German Democratic Republic patent specification 246 555, assigned to VEBLeuna-Werke "Walter Ulbricht," discloses a catalyst mixture comprisingerionite or LZ-40 type, alumina, platinum, and optionally rhenium.

None of the references disclose a physical mixture of a non-acidiclarge-pore zeolite comprising a platinum-group component and an acidicrefractory inorganic oxide having the absence of a platinum-group metal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved catalystsystem for the reforming of hydrocarbons. A corollary objective is toeffect aromatization of a paraffinic hydrocarbon feedstock with afavorable yield of gasoline-range product.

This invention is based on the discovery that catalytic reforming of anaphtha feedstock using a physical mixture of particles of platinum on anon-acidic L-zeolite and of an acidic inorganic oxide provide improvedactivity and/or yield of gasoline-range product.

A broad embodiment of the present invention is a catalyst systemcomprising a physical particle-form mixture of first particlescomprising a non-acidic large-pore zeolite and a platinum-group metaland second acidic particles comprising one or more inorganic oxides andhaving the absence of a platinum-group metal. The large-pore zeolitepreferably comprises L-zeolite, especially potassium-form L-zeolite. Thesecond particles generally have measurable Bronsted acidity,determinable by TMP MASNMR, and optimally comprise two or more inorganicoxides. Alumina is a preferred inorganic oxide, with boria and silicacomprising preferred alternative components of the second particles.Boria-alumina and silica-alumina are especially preferred components ofthe second particles.

In another aspect, the invention comprises a reforming process using acatalyst system comprising a physical mixture of first particlescomprising a non-acidic large-pore zeolite and a platinum-group metaland second particles comprising one or more inorganic oxides and havingthe absence of a platinum-group metal to upgrade a hydrocarbonfeedstock. Preferably, the process comprises aromatization of aparaffinic naphtha-range feedstock. Raffinate from aromatics extractionis an especially preferred feedstock.

These as well as other objects and embodiments will become apparent fromthe detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows ³¹ P proton-decoupled MASNMR spectra at TMP exposure forvarious boria-alumina samples.

FIG. 2 is a graph of the variation in conversion as a function oftemperature when reforming naphtha with a physical mixture of non-acidicL-zeolite and boria-alumina particles in comparison to a controlmixture.

FIG. 3 is a graph of C₅ + and methane yield from reforming as a functionof conversion for the same mixtures of the invention and the art asrepresented in FIG. 2.

FIG. 4 illustrates isopentane/n-pentane ratios of reforming product as afunction of conversion for the same mixtures as represented in FIG. 2.

FIG. 5 illustrates overall aromatics yields as a function of conversionfor the same mixtures as represented in FIG. 2.

FIG. 6 is a graph of the variation in conversion as a function oftemperature when reforming naphtha with a physical mixture of non-acidicL-zeolite and silica-alumina particles in comparison to a controlmixture.

FIG. 7 is a graph of C₅ + yield from reforming as a function ofconversion for the same mixtures of the invention and the art asrepresented in FIG. 6.

FIG. 8 illustrates C₅ + yield as a function of product octane number forthe mixtures represented in FIG. 2 and in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To reiterate, a broad embodiment of the present invention is directed toa catalyst system comprising a physical mixture of first particlescomprising a non-acidic large-pore zeolite and a platinum-group metaland second acidic particles comprising one or more inorganic oxides andhaving the absence of a platinum-group metal, and to a reforming processusing the catalyst system of the invention in a reforming process toupgrade a hydrocarbon feedstock.

The hydrocarbon feedstock comprises paraffins and naphthenes, and maycomprise aromatics and small amounts of olefins, boiling within thegasoline range. Feedstocks which may be utilized include straight-runnaphthas, natural gasoline, synthetic naphthas, thermal gasoline,catalytically cracked gasoline, partially reformed naphthas orraffinates from extraction of aromatics. The distillation range may bethat of a full-range naphtha, having an initial boiling point typicallyfrom 40°-80° C. and a final boiling point of from about 150°-210° C., orit may represent a narrower range within a lower final boiling point.Light paraffinic feedstocks, such as naphthas from Middle East crudeshaving a final boiling point of between about 80° and 150° C., arepreferred due to the specific ability of the process to dehydrocyclizeparaffins to aromatics. Raffinates from aromatics extraction, containingprincipally low-value C₆ -C₈ paraffins which can be converted tovaluable B-T-X aromatics, are especially preferred feedstocks.

The hydrocarbon feedstock to the present process contains small amountsof sulfur compounds, amounting to generally less than 10 parts permillion (ppm) on an elemental basis. Preferably the hydrocarbonfeedstock has been prepared from a contaminated feedstock by aconventional pretreating step such as hydrotreating, hydrorefining orhydrodesulfurization to convert such contaminants as sulfurous,nitrogenous and oxygenated compounds to H₂ S, NH₃ and H₂ O,respectively, which can be separated from the hydrotreated hydrocarbonsby fractionation. This conversion preferably will employ a catalystknown to the art comprising an inorganic oxide support and metalsselected from Groups VIB(6) and VIII(9-10) of the Periodic Table. SeeCotton and Wilkinson, Advanced Inorganic Chemistry, John Wiley & Sons(Fifth Edition, 1988)!. Good results are obtained with a catalystcontaining from about 5 to 15 mass % molybdenum or tungsten and fromabout 2 to 5 mass % cobalt or nickel. Conventional hydrotreatingconditions are sufficient to effect the needed degree of sulfur removalincluding a pressure of from about atmospheric to 100 atmospheres, atemperature of about 200° to 450° C., liquid hourly space velocity offrom about 1 to 20, and hydrogen to hydrocarbon mole ratio of betweenabout 0.1 and 10.

Alternatively or in addition to the conventional hydrotreating, thepretreating step may comprise contact with sorbents capable of removingsulfurous and other contaminants. These sorbents may include but are notlimited to zinc oxide, iron sponge, high-surface-area sodium,high-surface-area alumina, activated carbons and molecular sieves. Theart, including U.S. Pat. Nos. 4,028,223, 4,929,794, and 5,035,792 whichare incorporated herein by reference, teaches that a nickel sorbent iseffective for removing sulfur from hydrocarbons which subsequently areprocessed over a sulfur-sensitive catalyst. The nickel preferably issubstantially in reduced form and is combined with an inert binder toprovide a bed of particles; the nickel usually amounts to between 20 and90 mass %, preferably 30 to 70 mass %, of the total sorbent composite onan elemental basis. Excellent results are obtained with anickel-on-alumina sorbent, and alternative preferred binders compriseclay, kieselguhr, or silica. The nickel may be composited with thebinder by any effective means to provide active bound nickel, such ascoextrusion and impregnation. The composite of nickel and binder usuallyis calcined and reduced according to procedures known in the art. Asorbent pretreating step using the nickel sorbent generally is conductedin the liquid phase at between atmospheric and 50 atmospheres pressureand a temperature of between about 70° and 200° C., and optimallybetween 100° and 175° C. Liquid hourly space velocity can vary widelybetween about 2 and 50 depending on feed sulfur content, product sulfurand resulting sorbent utilization, desired run length and use of asingle or parallel swing beds. Preferably, the pretreating step willprovide the reforming catalyst with a hydrocarbon feedstock having lowsulfur levels disclosed in the prior art as desirable reformingfeedstocks, e.g., 1 ppm to 0.1 ppm (100 ppb). It is within the ambit ofthe present invention that the pretreating step be included in thepresent reforming process.

The reforming process contains a catalyst system comprising a physicalmixture of first particles comprising a non-acidic large-pore zeoliteand a platinum-group metal and second acidic particles comprising one ormore inorganic oxides and having the absence of a platinum-group metal.The particles can be thoroughly mixed using known techniques such asmulling to intimately blend the physical mixture. The mass ratio offirst particles to second particles depends on the nature of thefeedstock and the process objectives, and may range from about 1:10 to10:1. Preferably, a 100 cc sample of a contemporaneously mixed batchwill not differ in the percentage of each component of the mixturerelative to the batch by more than about 10%. Although the first andsecond particles may be of similar size and shape, the particlespreferably are of different size and/or density for ease of separationfor purposes of regeneration or rejuvenation following their use inhydrocarbon processing.

The first particles contain a non-acidic large-pore zeolite. Suitablezeolites generally have a maximum free-channel diameter or "pore size"of at least about 6 Å, and preferably have a moderately large pore sizeof about 7 to 8 Å as defined in the Atlas of Zeolite Structure Typesissued by the Structure Commission of the International ZeoliteAssociation. Such zeolites include, but are not limited to, thosecharacterized as BEA, FAU, LTL or MAZ structure type by the IUPACCommission on Zeolite Nomenclature, with the LTL structure or L-zeoliteof U.S. Pat. No. 3,216,789 being preferred. FAU is a favored alternativestructure, particularly the zeolite Y of U.S. Pat. Nos. 3,130,007;4,401,556; and 4,795,549 which are incorporated herein by referencethereto.

The first particles thus preferably comprise non-acidic L-zeolite and aplatinum-group metal component. It is essential that the L-zeolite benon-acidic, as acidity in the zeolite lowers the selectivity toaromatics of the finished catalyst. In order to be "non-acidic," thezeolite has substantially all of its cationic exchange sites occupied bynonhydrogen species. Preferably the cations occupying the exchangeablecation sites will comprise one or more of the alkali metals, althoughother cationic species may be present. An especially preferrednon-acidic L-zeolite is potassium-form L-zeolite.

Usually the L-zeolite is composited with a binder in order to provide aconvenient form for use in the catalyst of the present invention. Theart teaches that any refractory inorganic oxide binder is suitable. Oneor more of silica, alumina or magnesia are preferred binder materials ofthe present invention. One or both of amorphous silica and alumina areespecially preferred. Excellent results are obtained when using asynthetic white silica powder precipitated as ultra-fine sphericalparticles from a water solution. The silica binder preferably isnon-acidic, contains less than 0.3 mass % sulfate salts, and has a BETsurface area of from about 120 to 160 m² /g. The binder if presentcomprises from about 1 to 90 mass-% of the zeolite-binder composite, andpreferably from about 5 to 80 mass-% of the composite.

The L-zeolite and binder may be composited to form particle shapes knownto those skilled in the art such as spheres, extrudates, rods, pills,pellets, tablets or granules. Spherical particles may be formed directlyby the oil-drop method as disclosed hereinbelow or from extrudates byrolling extrudate particles on a spinning disk. In one method of formingextrudates, potassium-form L-zeolite and amorphous silica are commingledas a uniform powder blend prior to introduction of a peptizing agent. Anaqueous solution comprising sodium hydroxide is added to form anextrudable dough. The dough preferably will have a moisture content offrom 30 to 50 mass % in order to form extrudates having acceptableintegrity to withstand direct calcination. The resulting dough isextruded through a suitably shaped and sized die to form extrudateparticles, which are dried and calcined generally by known methods.Preferably, extrudates are subjected directly to calcination without anintermediate drying step in order to encapsulate potassium ions andpreserve basicity. The calcination of the extrudates is effected in anoxygen-containing atmosphere at a temperature of from about 260° to 650°C. for a period of about 0.5 to 2 hours.

An alternative alumina form of the present catalyst support is a sphere.Alumina spheres may be continuously manufactured by the well knownoil-drop method which comprises: forming an alumina hydrosol by any ofthe techniques taught in the art and preferably by reacting aluminummetal with hydrochloric acid; combining the resulting hydrosol with asuitable gelling agent; and dropping the resultant mixture into an oilbath maintained at elevated temperatures. The droplets of the mixtureremain in the oil bath until they set and form hydrogel spheres. Thespheres are then continuously withdrawn from the oil bath and typicallysubjected to specific aging and drying treatments in oil and anammoniacal solution to further improve their physical characteristics.The resulting aged and gelled particles are then washed and dried at atemperature of about 50° to about 205° C. and subjected to a calcinationprocedure at a temperature of about 450° to about 700° C. for a periodof about 1 to about 20 hours. This treatment effects conversion of thealumina hydrogel to the corresponding crystalline gamma-alumina. U.S.Pat. Nos. 2,620,314; 3,096,295; 3,496,115; 3,943,070; 4,273,735;4,514,511 and 4,542,113 provide additional details, and the productionof spherical catalyst particles by different methods is described inU.S. Pat. Nos. 4,514,511; 4,599,321; 4,628,040 and 4,640,807; thesepatents are incorporated herein by reference thereto.

An alkali metal component is a highly preferred constituent of the firstcatalyst particles. One or more of the alkali metals, including lithium,sodium, potassium, rubidium, cesium and mixtures thereof, may be used,with potassium being preferred. The alkali metal optimally will occupyessentially all of the cationic exchangeable sites of the non-acidicL-zeolite as described hereinabove. Surface-deposited alkali metal alsomay be present as described in U.S. Pat. No. 4,619,906, incorporatedherein by reference thereto.

The platinum-group metal component is another essential feature of thefirst particles, with a platinum component being preferred. The platinummay exist within the catalyst as a compound such as the oxide, sulfide,halide, or oxyhalide, in chemical combination with one or more otheringredients of the catalytic composite, or as an elemental metal. Bestresults are obtained when substantially all of the platinum exists inthe catalytic composite in a reduced state. The platinum componentgenerally comprises from about 0.05 to 5 mass % of the catalyticcomposite, preferably 0.05 to 2 mass %, calculated on an elementalbasis.

It is within the scope of the present invention that the catalyst maycontain other metal components known to modify the effect of thepreferred platinum component. Such metal modifiers may include GroupIVA(14) metals, Group VIIB(7) metals, other Group VIII(8-10) metals,rhenium, indium, gallium, zinc, uranium, dysprosium, thallium andmixtures thereof. Preferred modifiers include rhenium, indium, andnickel. Embodiment of such multimetallic catalysts are disclosed in U.S.Pat. Nos. 5,314,854 and 5,366,617, incorporated herein by reference.Catalytically effective amounts of such metal modifiers may beincorporated into the catalyst by any means known in the art. Generallythe metal modifier is present in a concentration of from about 0.01 to 5mass % of the finished catalyst on an elemental basis, with aconcentration of from about 0.05 to 2 mass % being preferred. The ratioof platinum-group metal to metal modifier is from about 0.2 to 20 on anelemental mass basis, and preferably is from about 0.5 to 10.

The final first particles generally will be dried at a temperature offrom about 100° to 320° C. for about 0.5 to 24 hours, followed byoxidation at a temperature of about 300° to 550° C. (preferably about350° C.) in an air atmosphere for 0.5 to 10 hours. Preferably theoxidized catalyst is subjected to a substantially water-free reductionstep at a temperature of about 300° to 550° C. (preferably about 350°C.) for 0.5 to 10 hours or more. The duration of the reduction stepshould be only as long as necessary to reduce the platinum, in order toavoid pre-deactivation of the catalyst, and may be performed in-situ aspart of the plant startup if a dry atmosphere is maintained. Furtherdetails of the preparation and activation of embodiments of the firstparticles are disclosed, e.g., in U.S. Pat. Nos. 4,619,906 (Lambert etal) and 4,822,762 (Ellig et al.), which are incorporated into thisspecification by reference thereto.

The second particles comprise a refractory inorganic oxide whichprovides acid sites for such reactions as isomerization and cracking. Itis believed, without limiting the invention, that Bronsted acidity is animportant characteristic of the second particles. Therefore, it ispreferable in characterizing the acidity of the second particles thatthe tests indicate the presence of Bronsted acidity.

A suitable test for determining the acidity of the second particlesinvolves the cracking of 1-heptene, as described in Example II. Thecomposites as 40-60 mesh particles are pretreated at 200° C. for 0.5 hrand 550° C. for 1 hr in a stream of hydrogen and loaded as a 250 mgsample into a microreactor. The test on 1-heptene is carried out at 425°C. at a base rate of 250 cc/min. Bronsted acidity is indicated by a highratio of propane and butane, generally at least about 80 mass-% andpreferably 90 mass-% or more, in the cracked products.

Acidity characteristics of the second particles also may be determinedby nuclear magnetic resonance, or NMR, and especially magic-anglespinning NMR, or MASNMR. Samples are loaded as powder in a glass tubeand pretreated under high vacuum (ca. 10⁻⁶) torr at 600° C. for 2 hr.The samples are cooled to 120° C., exposed to trimethylphosphine (TMP)for 15 min followed by a 45 min equilibration time, and then degassedwith high vacuum. The amount of adsorbed TMP is calculated from thevapor-pressure change after condensation on the samples from the knownvolume of vacuum line. The total integrated ³¹ P NMR signal intensitywas calculated for these samples based on the sample mass, number of NMRscans, and the signal size.

Other tests as known in the art, such as ammonia temperature-programmeddesorption (NH₃ TPD) and temperature-programmed pyridine absorbance ascharacterized by infrared spectra (pyridine TPD FT-IR) may be used tocharacterize the acidity of the second particles.

The second particles comprise a porous, adsorptive, high-surface-areamaterial, comprising one or more refractory inorganic oxides such asalumina, silica, titania, magnesia, zirconia, chromia, thoria, boria ormixtures thereof. It is within the scope of the present invention thatthe second particles further contain one or more of: (1) crystallinezeolitic aluminosilicates, either naturally occurring or syntheticallyprepared such as BEA, FAU, FER, LTL, MAZ, MEL, MFI, MOR, and MTW (IUPACCommission on Zeolite Nomenclature), in hydrogen form or in a form whichhas been exchanged with metal cations; (2) non-zeolitic molecularsieves, such as aluminophosphates and silicoaluminophosphates, includingbut not limited to structure types AEL, AFI, AFO and ATO; (3)synthetically prepared or naturally occurring clays and silicates, whichmay or may not be acid-treated, for example attapulgus clay,diatomaceous earth, fuller's earth, kaolin and kieselguhr; (4) spinelssuch as MgAl₂ O₄, FeAl₂ O₄, ZnAl₂ O₄, CaAl₂ O₄ ; and (5) combinations ofmaterials from one or more of these groups. Preferably the secondparticles comprise two or more refractory inorganic oxides selected fromalumina, boria, silica, titania and zirconia.

A preferred shape for the second particles is an extrudate. The wellknown extrusion method involves mixing the inorganic oxide and any othercomponents with a suitable peptizing agent to form a homogeneous doughor thick paste having a moisture content appropriate for the formationof extrudates with acceptable integrity to withstand direct calcination.Extrudability is determined from an analysis of the moisture content ofthe dough, with a moisture content in the range of from 30 to 50 wt. %being preferred. The dough is extruded through a die pierced withmultiple holes and cut to form particles in accordance with techniqueswell known in the art. A multitude of different extrudate shapes arepossible, including, but not limited to, cylinders, cloverleaf, dumbbelland symmetrical and asymmetrical polylobates. It is also within thescope of this invention that the uncalcined extrudates may be furthershaped to any desired form, such as spheres, by any means known to theart. Calcination of the extrudates is effected in an oxygen-containingatmosphere at a temperature of from about 260° to 650° C. for a periodof about 0.5 to 2 hours.

An alternative preferred form of the second particles is a sphere formedby use of the well known oil dropping technique substantially asdescribed hereinabove. The sphere preferably comprises alumina, whichpowder is converted into alumina sol by reaction with suitable peptizingacid and water. A mixture of the resulting sol and gelling agent isdischarged while still below gelation temperature by means of a nozzleor rotating disk into a hot oil bath maintained at or above gelationtemperature to form spherical particles of an alumina hydrogel which aresubjected to known aging, drying and calcination steps. This treatmenteffects conversion of the hydrogel to the corresponding inorganic oxidematrix.

A preferred refractory inorganic oxide comprises alumina, suitablyderived from any of the various hydrous aluminum oxides or alumina gelssuch as alpha-alumina monohydrate of the boehmite structure,alpha-alumina trihydrate of the gibbsite structure, beta-aluminatrihydrate of the bayerite structure, and the like. Gamma- oreta-alumina are particularly preferred. Favorable results are obtainedwith "Ziegler alumina," described in U.S. Pat. No. 2,892,858 andpresently available from the Vista Chemical Company under the trademark"Catapal" or from Condea Chemie GmbH under the trademark "Pural."Ziegler alumina is an extremely high-purity pseudoboehmite which, aftercalcination at a high temperature, has been shown to yield ahigh-priority gamma-alumina. It is especially preferred that therefractory inorganic oxide comprise substantially pure Ziegler aluminahaving an apparent bulk density of about 0.6 to 1 g/cc and a surfacearea of about 150 to 280 m² /g (especially 185 to 235 m² /g) at a porevolume of 0.3 to 0.8 cc/g. The inorganic oxide may be formed into anyshape or form of carrier material known to those skilled in the art suchas spheres, extrudates, rods, pills, pellets, tablets or granules.

In an especially preferred embodiment, the second particles comprisealumina and boria in a mass ratio of from about 1:1 to 100:1. The boriamay be composited with the alumina in any manner known in the art.Preferably, boria in the forms of B₂ O₃ or as tetra- or pyro-boric acidis admixed with the alumina sol before oil dropping or combined with thealumina-containing dough to extrusion. The combined oxides then areprocessed as described hereinabove to prepare the alumina-boria secondparticles. Optionally, the particles consist essentially of alumina andboria.

An alternative preferred embodiment of the second particles comprisessilica-alumina containing a weight ratio of silica to alumina of at fromabout 20:1 to about 1:100. Silica:alumina ratios of from about 4:1 up toabout 1:20 are preferred. An amorphous, cogelled, oil-droppedsilica-alumina is favored, prepared substantially as describedhereinabove for alumina spheres. Optimally an alumina sol, utilized asan alumina source, is commingled with an acidified water glass (sodiumsilicate) solution as a silica source, and the mixture is furthercommingled with a suitable gelling agent, for example, urea,hexamethylenetetraamine (HMT), or mixtures thereof. The mixture isdispersed into the hot oil bath as droplets which form into sphericalgel particles. The spheroidal gel particles may be atmospherically aged,usually in the oil bath, for a period of 6-16 hours, and then washed,preferably with an aqueous ammonia-ammonium nitrate solution, in asuitable alkaline or basic medium for at least 3 to about 10 hours, andfinally water rinsed. Pressure aging optionally may be employed toeffect a higher aging temperature at superatmospheric pressure in orderto maintain water in the liquid phase. The spheres are water-washed,preferably with water containing a small amount of ammonium hydroxideand/or ammonium nitrate. After washing, the spheres are dried at atemperature from about 85°-300° C. for a period from about 6 to about 24hours or more, and then calcined at a temperature from about 300°-760°C. for a period from about 2 to about 12 hours or more. The sodiumcontent optionally may be reduced by washing the oil-aged spheres withaqueous ammonium hydroxide-ammonium nitrate or washing the calcined basewith aqueous HCl, NH₄ NO₃, NH₄ Cl, HNO₃, (NH₄)N₃, for example. Exchangeof H⁺ for alkali metal may be accomplished by cycling the wash solutionthrough a packed bed of the calcined base followed by a water rinseusing techniques well known to the skilled worker.

The second particles are substantially free of platinum-group metals."Substantially free" is defined herein as containing less than about0.01 mass-% of a platinum-group metal, calculated on an elemental basis.Preferably the second particles are free of any metal component otherthan the inorganic oxides and molecular sieves disclosed above, and mostpreferably free of any metal other than those comprising alumina,magnesia, titania, zirconia and boria.

The second particles optionally may contain a halogen component. Thehalogen component may be either fluorine, chlorine, bromine or iodine ormixtures thereof. Chlorine is the preferred halogen component. Thehalogen component is generally present in a combined state with theinorganic-oxide support. The halogen component is preferably welldispersed throughout the particles and may comprise from more than 0.2to about 15 wt. %. calculated on an elemental basis, of the secondparticles. The particles suitably will be dried at a temperature of fromabout 100° to 320° C. for about 0.5 to 24 hours, followed by oxidationat a temperature of about 300° to 550° C. in an air atmosphere for 0.5to 10 hours.

In an alternative embodiment of the present invention, the physicalmixture of first particles comprising a non-acidic large-pore zeoliteand second acidic particles comprising an inorganic oxide is containedwithin the same catalyst particle. In this embodiment, the first andsecond particles may be ground or milled together or separately to formparticles of suitable size, preferably less than about 100 microns,which are supported in a suitable matrix. Optimally the matrix isselected from the inorganic oxides described hereinabove.

An optional embodiment of the present invention is a physical mixture ofthe catalyst system and a sulfur sorbent, i.e., a mixture of firstparticles, second particles and a sulfur sorbent. The sulfur sorbentshould not only be effective for removal of small amounts of sulfurcompounds from hydrocarbon streams at reforming-catalyst operatingconditions, but also be compatible with the components of the catalystsystem in order to maintain the activity of the catalyst. The sulfursorbent comprises a metal oxide, preferably selected from oxides of themetals having an atomic number between 19 and 30 inclusive; thesemetals, particularly potassium, calcium, vanadium, manganese, nickel,copper and zinc are known to be effective for sulfur removal in variouscircumstances. The sorbent optimally comprises a manganese component.Manganese oxide has been found to provide reforming catalyst protectionsuperior to the zinc oxide of the prior art, it is believed, due topossible zinc contamination of associated reforming catalyst. Themanganese oxides include MnO, Mn₃ O₄, Mn₂ O₃, MnO₃, and Mn₂ O₇. Thepreferred manganese oxide is MnO (manganous oxide). The manganesecomponent may be composited with a suitable binder such as clays,graphite, or inorganic oxides including one or more of alumina, silica,zirconia, magnesia, chromia or boria in order to provide a secondparticle for the physical mixture of the present catalyst system. Themanganese component preferably is unbound and consists essentially ofmanganese oxide, especially MnO.

The feedstock contacts the catalyst system of the invention in thereforming process in upflow, downflow, or radial-flow mode. Since thepresent reforming process operates at relatively low pressure, the lowpressure drop in a radial-flow reactor favors the radial-flow mode for areactor containing a single zone; a downflow reactor is favored when thereactor contains multiple zones. The catalyst or sorbent is contained ina fixed-bed reactor or in a moving-bed reactor whereby catalyst may becontinuously withdrawn and added. These alternatives are associated withcatalyst-regeneration options known to those of ordinary skill in theart, such as: (1) a semiregenerative unit containing fixed-bed reactorsmaintains operating severity by increasing temperature, eventuallyshutting the unit down for catalyst regeneration and reactivation; (2) aswing-reactor unit, in which individual fixed-bed reactors are seriallyisolated by manifolding arrangements as the catalyst become deactivatedand the catalyst in the isolated reactor is regenerated and reactivatedwhile the other reactors remain on-stream; (3) continuous regenerationof catalyst withdrawn from a moving-bed reactor, with reactivation andsubstitution of the reactivated catalyst, permitting higher operatingseverity by maintaining high catalyst activity through regenerationcycles of a few days; or: (4) a hybrid system with semiregenerative andcontinuous-regeneration provisions in the same unit. The preferredembodiment of the present invention is fixed-bed reactors in asemiregenerative unit.

Operating conditions used in the reforming process of the presentinvention include a pressure of from about 100 kPa to 6 MPa (absolute),with the preferred range being from about 100 kPa to 2 MPa and apressure of below 1 MPa being especially preferred. Hydrogen is suppliedto the reforming process in an amount sufficient to correspond to aratio of from about 0.1 to 10 moles of free hydrogen per mole ofhydrocarbon feedstock. The volume of the contained reforming catalystcorresponds to a liquid hourly space velocity of from about 1 to 40hr⁻¹. The operating temperature generally is in the range of 260° to560° C. Hydrocarbon types in the feed stock influence temperatureselection, as naphthenes generally are dehydrogenated over the reformingcatalyst with a concomitant decline in temperature across the catalystbed due to the endothermic heat of reaction. The temperature generallyis slowly increased during each period of operation to compensate forthe inevitable catalyst deactivation.

Since the predominant reaction occurring in the reforming process is thedehydrocyclization of paraffins to aromatics, this zone comprises two ormore reactors with interheating between reactors to compensate for theendothermic heat of reaction and maintain dehydrocyclization conditions.The reforming process produces an aromatics-rich effluent stream, withthe aromatics content of the C₅ + portion of the effluent typicallybeing within the range of about 45 to 85 mass-%. The composition of thearomatics depends principally on the feed-stock composition andoperating conditions, and generally comprises principally C₆ -C₁₂aromatics. Benzene, toluene and C₈ aromatics will be the primaryaromatics produced from the preferred light naphtha and raffinatefeedstocks.

Using techniques and equipment known in the art, thearomatics-containing reactor effluent usually is passed through acooling zone to a separation zone. In the separation zone, typicallymaintained at about 0° to 65° C., a hydrogen-rich gas is separated froma liquid phase. The resultant hydrogen-rich stream can then be recycledthrough suitable compressing means back to the reforming reactors. Theliquid phase from the separation zone is normally withdrawn andprocessed in a fractionating system in order to adjust the concentrationof light hydrocarbons and produce an aromatics-containing reformateproduct.

EXAMPLES

The following examples are presented to demonstrate the presentinvention and to illustrate certain specific embodiments thereof. Theseexamples should not be construed to limit the scope of the invention asset forth in the claims. There are many possible other variations, asthose of ordinary skill in the art will recognize, which are within thespirit of the invention.

Three parameters are especially useful in evaluating reforming processand catalyst performance, particularly in evaluating catalysts fordehydrocyclization of paraffins. "Activity" is a measure of thecatalyst's ability to convert reactants at a specified set of reactionconditions. "Selectivity" is an indication of the catalyst's ability toproduce a high yield of the desired product. "Stability" is a measure ofthe catalyst's ability to maintain its activity and selectivity overtime. The examples illustrate the effect of the invention especially onreforming catalyst activity and selectivity.

The same feedstock was used in all of the following tests, and had thefollowing characteristics:

    ______________________________________    Sp. gr.           0.736    ASTM D-86, °C.: IBP                      83    10%               93    50%               112    90%               136    EP                161    Mass %: Paraffins 60.4    Naphthenes        26.7    Aromatics         12.9    ______________________________________

Example I

A series of boria-alumina catalysts having a range of aluminum-to-boron("Al/B") ratios was prepared. In each case, starting materials comprisedaluminum nitrate and boric acid in a ratio to effect the Al/B ratiosshown below. The combination of aluminum nitrate and boric acid wascombined with distilled water and ammonium hydroxide to effect a pH ofabout 8. A boria-alumina precipitate was formed, recovered, and washedwith water. The washed precipitate was dried at 100° C. and calcined at600° C.

An extruded gamma alumina base of the prior art was prepared as acontrol for testing of the boria-alumina samples.

The calcined precipitates had the following characteristics:

    ______________________________________    Al/B, mole Surface Area m.sup.2 /g    ______________________________________    Composite A       1.2    185    Composite B       1.5    240    Composite C       1.6    250    Composite D       1.8    279    Composite E       2.6    379    Composite F       5.6    375    Composite G       14.2   356    Control X         ∞                             214    ______________________________________

Example II

The catalytic activity of the Example I composites was determined by a1-heptene reaction test. Each of the composites as 40-60 mesh particleswas pretreated at 200° C. for 0.5 hr and 550° C. for 1 hr in a stream ofhydrogen and loaded as a 250 mg sample into a microreactor. The test on1-heptene was carried out at 425° C. at a base rate of 250 cc/min. Mostof the conversion resulted in isomerized or cracked products, as shownbelow, along with a small amount of cyclization. Results were as followsin mass-%, averaging values at the beginning and ending of the test atthe 250 cc/min rate:

    ______________________________________            Conversion Isomerization                                  Cracking    ______________________________________    Composite A              49.4         40.2       8.8    Composite B              54.0         46.6       7.1    Composite C              73.0         63.2       9.4    Composite D              93.5         39.9       52.6    Composite E              94.0         35.4       57.4    Composite F              92.8         40.6       51.1    Composite G              63.3         51.6       10.0    Control X 55.5         44.5       3.1    ______________________________________

Propane and butane, indicative of Bronsted acidity, amounted to 93-95mass-% of the cracked products in all cases except for Composite G, forwhich the proportion was about 85 mass-%, and Control X, for which theproportion averaged about 37 mass-%.

Example III

The acidity of four of the samples was studied further via MagneticAngle Spinning Nuclear Magnetic Resonance (MASNMR). The ³¹ Pproton-decoupled MASNMR spectra at trimethylphosphine (TMP) exposurewere determined and are shown in FIG. 1. The amounts of TMP absorbed areas follows in mmol/g:

    ______________________________________           Composite A                   0.054           Composite B                   0.041           Composite F                   0.181           Composite G                   0.180    ______________________________________

The Bronsted acid site line near -5 ppm and the Lewis acid site linearound -45 to -50 ppm are clearly observed. Composites A and B show bothsmall Bronsted and Lewis acid sites, while Composite G shows a largerLewis acid site concentration. The intensity of the Bronsted acid siteline is largest for Composite F. Control X showed no Bronsted acidity byTMP MASNMR.

Example IV

Pilot-plant tests were carried out to determine the utility ofboria-alumina particles in a catalyst system of the invention comprisinga physical mixture of such particles with particles containing alarge-pore zeolite and platinum. The boria-alumina ratio wasintermediate to those of Composites E and F, having an Al/B molar ratioof about 3.3. The large-pore zeolite was potassium-form L-zeolite, andthe platinum content of the corresponding particles was about 0.8mass-%. The physical mixture of the invention comprised 80 mass-%platinum on L-zeolite and 20 mass-% boria-alumina.

A control mixture was prepared and tested using α-alumina, known to benearly neutral in acidity, and the same potassium-form L-zeolitecontaining 0.8% platinum as described above. The control physicalmixture comprised 80 mass-% platinum on L-zeolite and 20 mass-%α-alumina.

One reforming pilot-plant test was carried out on the physical mixtureof the invention and two tests were effected on the control mixture. Thenaphtha feedstock to reforming was as described above, and operatingconditions in each case were approximately as follows:

    ______________________________________    Pressure, atmospheres                         8    Hydrogen/hydrocarbon, mol                         8    Mass hourly space velocity, hr.sup.-1                         5    ______________________________________

Temperature was varied over each of the pilot-plant runs from 480° to525° C. at 15° C. intervals.

FIG. 2 shows the variation in conversion during each of the pilot-plantruns as a function of temperature. Conversion of naphthenes, which wasin the middle-to-upper 90% s in all cases, was higher for the catalystsystem of the invention at all temperatures. At each of thetemperatures, conversion of paraffins was sufficiently higher using thecatalyst system of the invention to result in a reduction of 15-20% inunconverted paraffins in the product compared to the control.

FIG. 3 shows a plot of C₅ + yield (yield of pentanes and heavierhydrocarbons) vs. conversion of total paraffins and naphthenes forcatalyst systems of the invention and the control. C₅ + yield for thecatalyst system of the invention averaged slightly lower values at lowerconversion and slightly higher at higher conversion than the control.

Also shown in FIG. 3 is a comparison of methane yield as a function ofconversion for the various catalyst systems. The mixture of theinvention shows a substantially lower methane yield, indicatingsubstantially less cracking to light gases according to the invention.

FIG. 4 compares isopentane/n-pentane ratios from the catalyst system ofthe invention and the control. The invention results in a substantiallyhigher iso- to normal-paraffin ratio, consistent with the desirabilityof isoparaffins in current reformulated gasolines.

FIG. 5 shows aromatics yields as a function of conversion. Aromaticsyields are substantially the same at higher conversion for the physicalmixture of the invention relative to the control, but average slightlylower at lower conversion. Benzene yield for the system of the inventionis 1-11/2% lower, and the invention thus results in an increase in therelative yield of alkylaromatics (e.g., xylenes).

Example V

Two silica-alumina composites having different ratios of silica toalumina were prepared, tested to determine acidity characteristics, andused in a physical mixture to reform naphtha.

Composite Y premix was prepared in the following manner. A solution of501 g water glass (30% SiO₂, 8.2% Na₂ O) and 250 g water was addeddropwise to a solution of 341 g 1:1 HCL containing 31.4 g urea powder.Al sol, 1.37 Al/Cl @ 15% Al, was added in an amount of 174 g, followedby 39 g of 42% hexamethylenetetramine, to the acidified water glasssolution.

Composite Z premix was prepared in the following manner. A solution of247 g water glass (30% SiO₂, 8.2% Na₂ O) and 280 g water was addeddropwise to a solution of 148 g 1:1 HCl containing 64 g urea powder. Alsol, 1.45 Al/Cl @ 14% Al, was added in an amount of 476 g to theacidified water glass solution.

Each of the Composites Y and Z premix was filtered, oil dropped and agedin oil at 95° C. for 18 hours. The spheres were subjected to adisplacement solution containing 0.5% NH₄ NO₃, then washed with watercontaining 0.5% NH₄ NO₃ and NH₃, dried at 100° C. and calcined at 650°C. in 3% steam.

Composite Y comprised silica and alumina in a mass ratio of about 75/25,and Composite Z comprised about 37 mass-% silica and 63 mass-% alumina.Conversion of 1-heptene with Composite Y according to the parameters ofExample II yielded the following results indicating the presence ofBronsted acidity:

    ______________________________________    Conversion        91.8%    Isomerization     41.6%    Cracking          48.6%    Propane and butane *                      88.5%    ______________________________________     * As a proportion of cracked product

Example VI

Pilot-plant tests were carried out to determine the utility ofsilica-alumina particles in a catalyst system of the inventioncomprising a physical mixture of such particles with particlescontaining a large-pore zeolite and platinum. Particles of bothComposite Y and Composite Z were tested. The large-pore zeolite waspotassium-form L-zeolite, and the platinum content of the correspondingparticles was about 0.8 mass-%. The physical mixture of the inventioncomprised 80 mass-% platinum on L-zeolite and 20 mass-% silica-alumina.

A control mixture comprising 80 mass-% platinum on L-zeolite and 20mass-% α-alumina was employed as discussed in Example IV.

One reforming pilot-plant test was carried out on the physical mixtureof the invention and compared with results when processing the controlmixture. The naphtha feedstock to reforming was as described above, andoperating conditions in each case were approximately as follows:

    ______________________________________    Pressure, atmospheres                         8    Hydrogen/hydrocarbon, mol                         8    Mass hourly space velocity, hr.sup.-1                         5    ______________________________________

Temperature was varied over each of the pilot-plant runs from 480° to525° C. at 15° C. intervals.

FIG. 6 shows the variation in conversion during each of the pilot-plantruns as a function of temperature. The plot is based on overallconversion of paraffins and naphthenes in the feedstock. Conversion wasclearly higher for the catalyst system of the invention, comprisingsilica-alumina Composites Y and Z, at all temperatures.

FIG. 7 shows a plot of C₅ + yield (yield of pentanes and heavierhydrocarbons) vs. conversion of total paraffins and naphthenes forcatalyst systems of the invention and the control. C₅ + yield was lowerparticularly at low conversion for the catalyst system comprisingComposite Y, but yields for the catalyst system comprising Composite Zwere comparable to those of the control.

Example VII

FIG. 8 is an expression of C₅ + product yields as a function of productoctane number for catalyst systems of the invention and the control. TheC₅ + yields are as shown in FIGS. 2 and 6, expressed to indicate ameasure of efficiency of gasoline production.

The higher activity of catalyst systems of the invention demonstratedfor catalyst systems of the invention is accompanied by more favorableyields at high severity when employing alumina-boria (3.3 Al/B) as theacidic component of the physical mixture. The high-silica Composite Yshowed lower yields as a function of product octane, but yieldefficiency for Composite Z in the mixture was comparable to that of thecontrol.

We claim:
 1. A catalyst system useful for the reforming of hydrocarbonscomprising a physical particle-form mixture of:(a) first particles of acatalytic composite comprising a non-acidic large-pore zeolite and aplatinum-group metal component; and, (b) second acidic particlesconsisting essentially of two or more refractory inorganic oxides andhaving the substantial absence of a platinum-group metal.
 2. Thecatalyst system of claim 1 wherein the second particles consistessentially of alumina and boria in a mass ratio respectively of fromabout 1:1 to 100:1.
 3. The catalyst system of claim 1 wherein the secondparticles comprise a halogen component.
 4. The catalyst system of claim1 wherein the catalyst system further comprises particles containing oneor more manganese oxides.
 5. A catalyst system useful for the reformingof hydrocarbons comprising a physical particle-form mixture of:(a) firstparticles of a catalytic composite comprising non-acidic L-zeolite, analkali-metal component and a platinum component; and, (b) secondparticles demonstrating the presence of Bronsted acidity and consistingessentially of alumina and one or more inorganic oxides selected fromthe group consisting of boria, silica, titania and zirconia.